The Trouble with Leap Years: A blog about why leap years are necessary.
Today is February 29, a date that appears on the calendar only once every four years. The reason for that is to balance out our calendar so that it reflects the actual time it takes the Earth to go around the sun. Otherwise, we’d be off by 24 days over the course of 100 years. And when certain holidays fall on certain days of the week would eventually get out of whack.
So how do you figure out if a year is a leap year? It’s pretty easy: If a year is divisible by 4, it’s a leap year. If it’s divisible by 100, it’s not. But if it’s divisible by 400, then it is again. So 2000 and 2400 are leap years, but 1800, 1900 and 2100 are not.
If you add up all the days in all the months each year for four years (including an extra day for each leap year), you’ll find that there are 1461 days, or exactly four times 365 days (or 366 x 4 – 1). That means that every four years we’ve got an extra day tacked onto February to balance everything out. This process repeats itself throughout history – hence why leap
The trouble with leap years is that they add an extra day every four years. As it turns out, this is a problem because the Earth doesn’t really orbit around the sun in exactly 365 days. It actually takes 365 days, 5 hours, 48 minutes, and 46 seconds.
We get away with this seemingly inaccurate calculation by adding a leap day every four years to make up for the fraction of a day that we lost in the previous three years. This is why we call it a leap year. An extra day is added to keep the calendar year synchronized with the solar year or astronomical year (which is also known as the true year).
In general, if a year is divisible by 4, then it’s a leap year except if it’s also divisible by 100 then it’s not a leap year unless it’s also divisible by 400.
Why does this weird rule work? Well, for one thing, the average length of our calendar year is still very close to 365.25 days which is decent enough considering how much of an improvement this leap year rule was over the old Julian Calendar system that we used to have before 1582 (which was way off with its 365.25-day average).
In many ways the world is a much simpler place than it used to be. Each day we have less to worry about, in part because so many things are now computerized. But this has a downside: when a computer fails, it often takes our lives down with it.
Today we can look forward to the added day of February 29th as Leap Day. But every four years, something in our digital lives goes slightly awry.
In spite of the extra day, a full year still consists of 365 days, or 8,760 hours (24 * 365). So what’s the problem? Today’s calendar was developed by Julius Caesar over 2,000 years ago, and was refined by Pope Gregory XIII in 1582. The calendar works great for most astronomical phenomena because it makes every fourth year a leap year with 366 days. This keeps the calendar aligned with the Earth’s revolutions around the Sun.
However, there is still a slight discrepancy between our calendar and the actual number of days in a year: 1/100th of a day per year. After 100 years this adds up to roughly three-quarters of a day (0.75). After 400 years that’s three days (3), and after 8,000 years that’s 22 days (22
In this blog we will be discussing the reasons why you should always check if a year is a leap year before attempting to calculate the date of an event that occurs on 29th February.
In the Gregorian calendar, years evenly divisible by 4 are leap years, with the exception of centurial years that are not evenly divisible by 400. For example, the years 1700, 1800, and 1900 were not leap years, but the year 2000 was.
The function below takes a year as input and returns True if the year is a leap year, False otherwise. It assumes that the input is of type int and uses modulo division.**
At one time, the Gregorian calendar was called the “improved calendar of Pope Gregory”. This calendar is more accurate than the old Julian calendar which was replaced throughout most Christian countries in 1582. It is based on the assumption that Earth revolves around the Sun in exactly 365 days, 5 hours, 49 minutes and 12 seconds, or 365.2425 days per year.
However, even this slightly-modified solar year of 365.2425 days does not fit into a whole number of weeks (7 days), months (28, 30 or 31 days) or years (365 days) without some adjustments.
The problem is that it takes the Earth just over 365.2425 days to complete a full orbit around the Sun each year. This means that if we did not add an extra day every four years, we would lose about 6 hours off our calendar every year. After only 100 years, our calendar would be off by around 24 days! And after 200 years it would be almost a month behind and so on…